The present invention relates generally to separation systems for launch vehicles, and more particularly, to variable spacers for use in such systems.
Separation systems are typically integrated in launch vehicles for use during both spacecraft separation and fairing separation. As is widely known, launch vehicles are used to transport spacecrafts from the Earth""s surface into space. Separation systems are typically used to secure the spacecrafts to the launch vehicles during lift-off and ascent. These systems then subsequently detach the spacecrafts from the launch vehicles during spacecraft separation. The separation systems may also be used to secure the fairings of the launch vehicles and then subsequently detach the fairings from each other during fairing separation.
Separation systems use separation bolts and fragmentary separator nuts to attach the spacecrafts to the payload attach fittings of the launch vehicles. A single spacecraft is typically attached to a payload attach fitting by employing a nut and bolt on one side of the spacecraft, with a nut and bolt being located at each corner of that side.
Torque is typically applied to the bolt or the nut to preload a separation bolt. Where a conventional bolt is used, the amount of preload is determined by merely specifying the amount of torque applied. Alternatively, where an instrumented bolt is used, the amount of preload is determined by measuring the strain output.
The separation bolts are typically preloaded so as to prevent an occurrence of gapping between mating surfaces of the spacecraft and the payload attach fitting. Gapping can be caused by acceleration forces experienced by the spacecraft primarily during lift-off and ascent. Gapping results in slight movement of the spacecraft with respect to the launch vehicle. This movement may exacerbate vibrations typically experienced by the spacecraft during liftoff and ascent. To prevent gapping and its adverse effects, a sufficient amount of preload is applied to the bolts. A typical amount of preload must exceed forces in the separation bolt caused by maximum accelerations experienced by the spacecraft.
Unfortunately, existing separation bolts remain preloaded during spacecraft separation and fairing separation. Spacecraft separation and fairing separation occur well beyond the time period usually necessary to prevent gapping. As is known, spacecraft separation occurs when the launch vehicle reaches a destination in space where the spacecraft is released. For example, spacecraft separation for a satellite usually occurs at the location where the launch vehicle reaches the desired orbit level of the satellite. During spacecraft separation, the separation system typically uses an ordinance device to force the fragmentary separator nut into three pieces thereby releasing the separation bolt and the spacecraft.
Likewise, fairing separation typically occurs when the launch vehicle is outside the atmosphere. During fairing separation, an ordinance device typically forces the fragmentary separator nut into three separate pieces thereby releasing the fairing.
Forcing the fragmentary separator nut into pieces suddenly releases the preloaded energy stored within the bolt. This abrupt release of energy may result in unacceptable levels of shock that can cause damage to the launch vehicle and the spacecraft. Such a result is obviously undesirable.
Therefore, a need exists to secure a spacecraft to a launch vehicle so as to prevent gapping during a turbulent stage while avoiding unacceptable shock levels during spacecraft separation.
It is therefore an object of the present invention to prevent an occurrence of gapping between mating surfaces of a spacecraft and a launch vehicle during periods of high dynamic loading on the spacecraft. Another object of the present invention is to reduce shock levels experienced during spacecraft separation. It is yet another object of the present invention to prevent an occurrence of gapping between mating surfaces of a fairing and a launch vehicle during periods of high dynamic loading on the launch vehicle. It is still another object of the present invention to reduce shock levels experienced during fairing separation.
In accordance with the above and other objects of the present invention, a variable spacer has been provided. The variable spacer includes a plate having a first surface and a second surface. The plate has at least one hole integrally formed therein, extending from the first surface to the second surface. The hole receives a separation bolt therein for attaching a first wall to a second wall. Torque is applied to the separation bolt for providing a first load therein. Then, the variable spacer is used to increase the first load to a second load during a turbulent stage. The second load prevents an occurrence of gapping at an attachment point between the first wall and the second wall during periods of high dynamic loading. The plate also reduces the second load to a third load during a separation stage. The third load decreases a shock level experienced by the launch vehicle and the payload transported by the launch vehicle.
Additional advantages and features of the present invention will become apparent from the description that follows, and may be realized by means of the instrumentalities and combinations particularly pointed out in the appended claims, taken in conjunction with the accompanying drawings.